title: Factors influencing the release of purines and norepinephrine in the rabbit portal vein.
abstract: Previous studies have shown that transmural electrical stimulation (TES) of the rabbit portal vein in vitro, results in the overflow of 3H-purines from tissues prelabelled with 3H-adenosine. The purpose of the present study was to assess the possible sites which contribute to the TES-induced overflow of purines in this adrenergically innervated tissue. The contribution to postjunctional elements to purine overflow was assessed with the alpha 1-adrenoceptor antagonist, prazosin. Prazosin (3 x 10(-7) M) did not affect the release of 3H-norepinephrine but markedly reduced the TES-induced contraction. The release of 3H-purines was reduced by 20% by prazosin, indicating that approximately 80% of the release is independent of the alpha 1-mediated postjunctional response and, therefore, probably originates from neuronal sites in the tissue. Two lines of evidence indicate that a considerable portion of the alpha 1-adrenoceptor-independent release of 3H-purines (i.e., in the presence of prazosin) arises from adrenergic nerves. First, the fractional release of 3H-purines was enhanced and reduced, respectively, by the alpha 2-adrenoceptor antagonist, yohimbine, and the alpha 2-adrenoceptor agonist, clonidine, in concentrations (10(-6) M) which did likewise to the fractional release of 3H-norepinephrine. Second, destruction of the adrenergic nerves by in vitro treatment with 6-hydroxydopamine reduced the fractional release of 3H-purines by 55%. The release of purines which remains after 6-hydroxydopamine treatment may occur from non-adrenergic nerves.
mesh_terms: D000320:Adrenergic Fibers / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004558:Electric Stimulation; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009638:Norepinephrine / Q000378:metabolism*; D016627:Oxidopamine; D011169:Portal Vein / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D011687:Purines / Q000378:metabolism*; D011817:Rabbits; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D006892:Hydroxydopamines; D011687:Purines; D015016:Yohimbine; D016627:Oxidopamine; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin